Electrographic development method and apparatus

ABSTRACT

The invention relates generally to processes for electrographic image development. An electrographic development apparatus is provided wherein a film is adjacent a cylindrical toning shell and a mixture of toner and carrier is particles disposed on the cylindrical toning shell in contact with the film. The cylindrical toning shell is closest to the film at a first location, the mixture of toner and carrier particles being movable through the first location with a flow direction. A magnetic core disposed within the cylindrical toning shell offset toward the cylindrical shell such that a magnetic field strength is greater at the second location than the first location.

BACKGROUND

The invention relates generally to processes for electrographic imagedevelopment.

Processes for developing electrographic images using dry toner are wellknown in the art and are used in many electrographic printers andcopiers. The term “electrographic printer,” is intended to encompasselectrophotographic printers and copiers that employ a photoconductorelement, as well as ionographic printers and copiers that do not relyupon a photoconductor. Electrographic printers typically employ adeveloper having two or more components, consisting of resinous,pigmented toner particles, magnetic carrier particles and othercomponents. The developer is moved into proximity with an electrostaticimage carried on an electrographic imaging member, whereupon the tonercomponent of the developer is transferred to the imaging member, priorto being transferred to a sheet of paper to create the final image.Developer is moved into proximity with the imaging member by anelectrically-biased, conductive toning shell, often a roller that may berotated co-currently with the imaging member, such that the opposingsurfaces of the imaging member and toning shell travel in the samedirection. Located adjacent the toning shell is a multipole magneticcore, having a plurality of magnets, that may be fixed relative to thetoning shell or that may rotate, usually in the opposite direction ofthe toning shell.

The developer is deposited on the toning shell and moved into proximitywith the imaging member, at a location where the imaging member and thetoning shell are in closest proximity, referred to as the “toning nip.”In the toning nip, the magnetic carrier component of the developer formsa “nap,” similar in appearance to the nap of a fabric, on the toningshell, because the magnetic particles form chains of particles that risefrom the surface of the toning shell in the direction of the magneticfield.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 presents a schematic of an apparatus for developing anelectrographic image, according to an aspect of the invention.

FIG. 2 presents a schematic of a magnetic core and toning shell with arepresentation of a magnetic field, according to a further aspect of theinvention.

FIG. 3 presents a schematic of magnetic field strength around the toningshell outer circumference, according to a further aspect of theinvention.

FIG. 4 presents a schematic of an apparatus for developing anelectrographic image, according to an aspect of the invention.

FIG. 5 presents a schematic of a magnetic core and toning shell with arepresentation of a magnetic field, according to a further aspect of theinvention.

FIG. 6 presents a schematic of magnetic field strength around the toningshell outer circumference, according to a further aspect of theinvention.

FIG. 7 presents a cross-sectional view of an apparatus for developing anelectrographic image, according to an aspect of the invention.

DETAILED DESCRIPTION

Various aspects of the invention are presented in FIGS. 1-7, which arenot drawn to any particular scale, and wherein like components in thenumerous views are numbered alike. As used herein, the terms“comprising”, “having”, and “including” are intended to have anopen-ended meaning. Referring-now specifically to FIG. 1, anelectrographic development apparatus 100 is presented, according to anaspect of the invention. Apparatus 100 comprises a film 10 and acylindrical toning shell 12 having an toning shell outer circumference14. A mixture of toner and carrier particles 16 is disposed on thecylindrical toning shell 12 in contact with the film 10. The cylindricaltoning shell 12 is closest to the film at a first location 20, themixture of toner and carrier particles 16 being movable through thefirst location with a flow direction 18. With reference to FIGS. 2 and3, a magnetic core 22 is disposed within the cylindrical toning shell 12that provides a magnetic field strength of varying magnitude around thetoning shell outer circumference 14, the magnetic field strength havinga first time-averaged absolute magnitude 26 at the first location 18,and a second time-averaged absolute magnitude 28 at a second location 30a distance 32 from the first location 20 in the flow direction 18. Thesecond time-averaged absolute magnitude 28 is greater than the firsttime-averaged absolute magnitude 26.

According to an aspect of the invention, the second time-averagedabsolute magnitude 28 is at least 25 gauss greater than the firsttime-averaged absolute magnitude 26, or at least 50 gauss greater thanthe first time-averaged absolute magnitude 26, or at least 70 gaussgreater than the first time-averaged absolute magnitude 26, or at least100 gauss greater than the first time-averaged absolute magnitude 26, orat least 125 gauss greater than the first time-averaged absolutemagnitude 26. According to a further aspect of the invention, the secondtime-averaged absolute magnitude 28 is at least 2.5% greater than thefirst time-averaged absolute magnitude 26, or at least 5% greater thanthe first time-averaged absolute magnitude 26, or at least 7% greaterthan the first time-averaged absolute magnitude 26, or at least 10%greater than the first time-averaged absolute magnitude 26, or at least125% greater than the first time-averaged absolute magnitude 26.According to an aspect of the invention, increasing the magnetic fieldstrength differential tends to decrease toning potential withoutincreasing developer pick-up on the film.

The film 10 is any of the type known in the electrographic arts capableof carrying an electrostatic image, for example anelectrophotoconductive film of the type generally used inelectrophotographic image development. The film 10 is moved past thefirst location 20 in a film direction 34 with a film speed, as is wellknown in the art, using a known structure such as a film loop. The filmtypically comprises a ground reference 36, and a voltage V1 is appliedto the toning shell 14 in order to generate an electrical field in theregion of the first location 20 (the “toning nip”) that draws or repelstoner to the surface of the film 12 depending upon the charge carried bythe film 12. In such manner, an electrostatic image is developed. Theinvention may be used with both Charged Area Development, and DischargedArea Development, as is described in U.S. Pat. No. 6,526,247 issued Feb.25, 2003, to Stelter, Guth; Regelsberger and Eck, the contents of whichare incorporated by reference as if set forth herein. The voltage V1 maybe a static voltage and may have a superimposed alternating componentthat assists toning of the electrostatic image. A scavenger 42 mayprovided on the downstream side (in the flow direction 18) of the firstlocation 20, that may be adjacent the second location 30, and is chargedwith a second voltage V2. An electrical field develops that assists inremoving carrier particles adhering to film 10 since the film 10 isgrounded through the ground reference 36. A skive 46 may be provided tometer the mixture of toner and carrier particles 16 onto the cylindricaltoning shell 12.

Referring now to FIG. 2, the magnetic core 22, toning shell 12 are shownwith a magnetic field 24. The magnetic core 22 comprises a plurality ofmagnets 44 that generate the magnetic field 24, B (the correspondinglines inside the magnetic core 22 are not shown). The magnitude of themagnetic field varies from positive to negative depending upon itsdirection. Referring now to FIG. 3, the absolute magnitude of B, thescalar quantity |B|, at the surface of the toning shell, is presentedversus position around the toning shell outer circumference 14. Thesecond time-averaged absolute magnitude 28 may be a maximumtime-averaged absolute magnitude of magnetic field strength around thetoning shell outer circumference 14, as is shown in FIG. 3, althoughthis is not necessary in the practice of the invention.

In the example presented in FIGS. 1-3, the magnetic core 22 is fixed,cylindrical and concentric with the cylindrical toning shell 12, themagnet 48 is the strongest of the magnets 44, and the cylindrical toningshell 12 is rotated. As such, the magnetic field 24 at a given fixedlocation, for example first location 20 and second location 30, does notchange as a function of time. Therefore the time-averaged absolutemagnitude of the magnetic field strength is simply the absolutemagnitude of the field strength at a given location. As will bediscussed in more detail below, the magnetic core 22 may be rotated. Insuch case, the absolute magnitude of the magnetic field strength variesas a function of time and is time-averaged. The term “time-averagedabsolute magnetic field strength” is intended to encompass time-varyingand time-non-varying magnetic fields.

The carrier particles may comprise hard magnetic carrier particles. Insuch case, the magnetic brush may operate according to the principlesdescribed in U.S. Pat. Nos. 4,473,029 and 4,546,060, the contents ofwhich are fully incorporated by reference as if set forth herein. Thetwo-component dry developer composition of U.S. Pat. No. 4,546,060comprises charged toner particles and oppositely charged, magneticcarrier particles, which (a) comprise a magnetic material exhibiting“hard” magnetic properties, as characterized by a coercivity of at least300 gauss and (b) exhibit an induced magnetic moment of at least 20EMU/gm when in an applied field of 1000 gauss, is disclosed. Asdescribed in the '060 patent, the developer is employed in combinationwith a magnetic applicator comprising a rotatable magnetic core and anouter, nonmagnetizable shell to develop electrostatic images. When hardmagnetic carrier particles are employed, exposure to a succession ofmagnetic fields emanating from the rotating core applicator causes theparticles to flip or turn to move into magnetic alignment in each newfield. Each flip, moreover, as a consequence of both the magnetic momentof the particles and the coercivity of the magnetic material, isaccompanied by a rapid circumferential step by each particle in adirection opposite the movement of the rotating core. The observedresult is that the developers of the '060 flow smoothly and at a rapidrate around the shell while the core rotates in the opposite direction,thus rapidly delivering fresh toner to the photoconductor andfacilitating high-volume copy and printer applications.

The mixture of toner and carrier particles 16 is typically movable byrotating either the cylindrical toning shell 12, or by rotating themagnetic core 22, or by rotating both the cylindrical toning shell 12and the magnetic core 22 in the same or opposite directions. Thecylindrical toning shell 12 or the magnetic core 22 may be fixed. Withsoft magnetic carriers, for example and without limitation, the magneticcore 22 may be fixed and the cylindrical toning shell 12 may be rotatedin order to move the mixture of carrier and toner particles 16 intocontact with the film 10 (“soft magnetic carriers” meaning magneticcarriers excluded by the definition of “hard magnetic carriers” setforth above).

Referring now to FIGS. 4, 5 and 6, an apparatus 200 is presented similarto apparatus 100, except the magnetic core 22 is offset toward thecylindrical toning shell 12 such that the magnetic core 22 is closest tothe cylindrical toning shell 12 at the second location 30. The magneticcore 22 may be cylindrical, and may comprise an outer magnetic corecircumference 38 and a multitude of magnets 40 of uniform strength withalternating north and south poles disposed around the outer magneticcore circumference 38. In this example, the magnetic field varyingmagnitude around the toning shell outer circumference 14 is generated bythe offset toward the cylindrical toning shell 12, as best shown in FIG.5. Offsetting the magnetic core 22 toward the cylindrical shelldownstream from the toning nip (a distance 32 in the direction ofdeveloper flow 18 through the first location 20) preferably increasesthe strength of the magnetic field on the downstream side and assistswith removing carrier particles adhered to the film 10 and returningthem to the mixture of developer and carrier particles 16. In a certainembodiment, the magnetic core 22 is disposed within the cylindricaltoning shell 12 offset toward the cylindrical toning shell 12 such thatthe magnetic core 22 is closest to the cylindrical toning shell at thesecond location 30 the distance 32 from the first location 20 in theflow direction 18. The scavenger 42 may be provided to further assistwith scavenging in order to minimize developer pick-up. Furthermore,offsetting the magnetic core 22 in the manner described herein maydecrease the strength of the electrical field needed for adequate imagedevelopment at the first location 20.

According to a further aspect of the invention, the cylindrical toningshell 12 and the magnetic core 22 (in this case cylindrical), are notconcentric. The geometric center of the magnetic core 22 may be offsetrelative to the geometric center of the cylindrical toning shell 12 inthe flow direction 18 an offset distance. This may be combined with anoffset toward the first location 20. A line from the first location tothe center of rotation to the second location may define an acute angleα greater than 20 degrees, at least 30 degrees, at least 45 degrees, orat least 60 degrees. This also applies to the position of the secondlocation relative to the first location in FIG. 1.

According to a further aspect of the invention, an electrographicdevelopment method is provided, comprising moving the mixture of tonerand carrier particles 16 disposed on the cylindrical toning shell 22 incontact with a film 10 in the flow direction 18 through a first location20 wherein the cylindrical toning shell 12 is closest to the film 10,the magnetic core 22 being disposed within the cylindrical toning shell12 that provides the magnetic field strength of varying magnitude aroundthe toning shell outer circumference 14, the magnetic field strengthhaving a first time-averaged absolute magnitude at the first location20, and a second time-averaged absolute magnitude 30 at the secondlocation 30 a distance from the first location 20 in the flow direction18, the second time-averaged absolute magnitude being greater than thefirst time-averaged absolute magnitude.

According to a further aspect of the invention, an electrographicdevelopment method is provided, comprising moving the mixture of tonerand carrier particles 16 disposed on the cylindrical toning shell 22 incontact with a film 10 in the flow direction 18 through a first location20 wherein the cylindrical toning shell 12 is closest to the film 10,the magnetic core 22 being disposed within the cylindrical toning shell12, the magnetic core 22 being disposed within the cylindrical toningshell 12 offset toward the cylindrical toning shell 12 such that themagnetic core is closest to the cylindrical toning shell at a secondlocation 30 a distance 32 from the first location 20 in the flowdirection 18.

Referring now to FIG. 7, a cross-sectional view of an electrographicdeveloping apparatus 300 is presented implementing an blender 10according to the invention. Toning station 300 comprises a housing 302that defines a developer sump 304 containing a developer (not shown)that is a mixture of toner and hard magnetic carriers of a typedescribed in U.S. Pat. No. 4,546,060. A ribbon blender 306 is rotated inthe sump 304. The ribbon blender mixes and agitates the developerkeeping it well mixed and also promoting tribocharging of the carrierand toner particles constituting the developer. A developer feedmechanism 308 lifts developer from the sump 304 to a magnetic brush 310.The magnetic brush is of a type described in U.S. Pat. No. 4,546,060 andcomprises a toning shell 312 configured to rotate, and a core 314 havinga plurality of magnets of alternating polarity that upon rotation of thecore 314 cause the carrier particles to rotate in an opposite directionin an advancing nap coating the toning shell 312, as is well known inthe art. The toning shell 312 may be rotated to contribute to the motionof the nap, again, as is well known in the art.

The advancing nap (not shown), constituting a magnetic brush, contacts afilm 316 having a latent electrostatic image, generally a photoconductoras is known in the electrophotographic arts, and toner is attracted fromthe magnetic brush (developer) to the film 316 as it is advanced overthe magnetic brush, thereby developing the image thereon. A backer bar318 retains the film 316 in proper position relative to the toningshell, and in contact with the magnetic brush. The developer falls backinto the sump 304. The blender according to the invention is preferablyformed from a metal, for example aluminum.

The toner particles may comprise MICR (Magnetic Ink CharacterRecognition) toner particles. A suitable MICR toner is described in U.S.Pat. No. 6,610,451 entitled “DEVELOPMENT SYSTEMS FOR MAGNETIC TONERSHAVING REDUCED MAGNETIC LOADINGS”, with about 23% iron oxide and 8%olfeinic wax by weight, and a silica surface treatment. The U.S. Pat.No. 6,610,451 is incorporated by reference as if fully set forth herein.A polymethylmethacrylate surface treatment may also be implemented, forexample catalogue number MP1201 available from Soken Chemical &Engineering Co., Ltd., Tokyo, Japan, and distributed by EsprixTechnologies of Sarasota, Fla. The carrier particles may be SrFe12O19coated with polymethylmethacrylate. Volume mean diameter of 20.5 microns(sigma=0.7 microns for ten production runs of a carrier material),measured using an Aerosizer particle sizing apparatus (TSI Incorporatedof Shoreview, Minn.). A suitable carrier has a coercivity of 2050 Gauss,a saturation magnetization of 55 emu/g, and a remnance of 32 emu/g,measured using an 8 kG loop on a Lake Shore Vibrating SampleMagnetometer (Lake Shore Cryotronics, Inc., of Westerville, Ohio).

The sump in an electrographic developing apparatus 300 may have anaverage roughness of ten readings of 70 microinches Ra±20, with none ofthe ten readings being less than 20 microinches Ra or more than 120microinches Ra, and 35 microinches Ra in the area of the toner monitor.The apparatus 300 may comprise a ribbon blender having an outsidediameter of 2.760 inch, a toning shell having an outside diameter of1.996 inch, a magnetic core of 1.700 inch. The magnetic core may have 14magnets, a maximum magnetic field strength of 950 gauss and a minimummagnetic field strength of 850 gauss. At 110 pages per minute the ribbonblender may rotate 355 RPM, the toning shell may rotate at 129.1 RPM,and the magnetic core may rotate at 1141 RPM. At 150 pages per minutethe ribbon blender may rotate 484 RPM, the toning shell may rotate at176 RPM, and the magnetic core may rotate at 1555.9 RPM. The magneticcore may be shifted 0.050 inch toward the toning shell, and 0.050 inchin the flow direction (perpendicular to the shift toward the toningshell). Of course, other shifts are contemplated in the practice of theinvention, for example 0.023 inch toward the toning shell, and 0.023inch in the flow direction (perpendicular to the shift toward the toningshell).

In operating the apparatus 300 with MICR toner, the voltage V1 mayconfigured as a bias on the order of 86 volts relative to the filmcharging potential, the film charging potential generally being in therange of 300-750 volts and discharging to a voltage on the order of 100volts upon exposure to an infrared light emitting diode. The toner isfused at a temperature on the order of 375 degrees F., and the developermay be exercised for a period of time on the order of 1.5 minutes priorto initializing toning in order to reduce densification. The scavengermay be charged with a voltage V2 on the order of 900 volts DC with 600volts AC superimposed.

Although the invention has been described and illustrated with referenceto specific illustrative embodiments thereof, it is not intended thatthe invention be limited to those illustrative embodiments. Thoseskilled in the art will recognize that variations and modifications canbe made without departing from the true scope and spirit of theinvention as defined by the claims that follow. It is therefore intendedto include within the invention all such variations and modifications asfall within the scope of the appended claims and equivalents thereof.

1. An electrographic development apparatus, comprising: a film; acylindrical toning shell having an toning shell outer circumference; amixture of toner and carrier particles disposed on the cylindricaltoning shell in contact with the film, the cylindrical toning shellbeing closest to the film at a first location, the mixture of toner andcarrier particles being movable through the first location with a flowdirection; a magnetic core disposed within the cylindrical toning shellthat provides a magnetic field strength of varying magnitude around thetoning shell outer circumference, the magnetic field strength having afirst time-averaged absolute magnitude at the first location, and asecond time-averaged absolute magnitude at a second location a distancefrom the first location in the flow direction, the second time-averagedabsolute magnitude being greater than the first time-averaged absolutemagnitude; and a scavenger adjacent the second location.
 2. Theapparatus of claim 1, wherein the second time-averaged absolutemagnitude is a maximum time-averaged absolute magnitude of magneticfield strength around the toning shell outer circumference.
 3. Theapparatus of claim 1, wherein the magnetic core is either fixed orrotatable.
 4. The apparatus of claim 1, wherein the cylindrical toningshell is either fixed or rotatable.
 5. The apparatus of claim 1, whereinthe magnetic core is cylindrical, comprising an outer magnetic corecircumference and a multitude of magnets of uniform strength withalternating north and south poles disposed around the outer magneticcore circumference.
 6. The apparatus of claim 5, wherein the magneticcore is offset toward the cylindrical toning shell such that themagnetic core is closest to the cylindrical toning shell at the secondlocation.
 7. The apparatus of claim 1, wherein the carrier particlescomprise hard magnetic carrier particles.
 8. The apparatus of claim 1,wherein the toner particles comprise MICR toner particles.
 9. Anelectrographic development apparatus, comprising: a film; a cylindricaltoning shell having an toning shell outer circumference; a mixture oftoner and carrier particles disposed on the cylindrical toning shell incontact with the film, the cylindrical toning shell being closest to thefilm at a first location, the mixture of toner and carrier particlesbeing movable through the first location with a flow direction; and, amagnetic core disposed within the cylindrical toning shell that providesa magnetic field strength of varying magnitude around the toning shellouter circumference, the magnetic field strength having a firsttime-averaged absolute magnitude at the first location, and a secondtime-averaged absolute magnitude at a second location a distance fromthe first location in the flow direction, the second time-averagedabsolute magnitude being at least 25 gauss greater than the firsttime-averaged absolute magnitude.
 10. The apparatus of claim 9, thesecond time-averaged absolute magnitude being at least 50 gauss greaterthan the first time-averaged absolute magnitude.
 11. The apparatus ofclaim 9, the second time-averaged absolute magnitude being at least 75gauss greater than the first time-averaged absolute magnitude.
 12. Theapparatus of claim 9, the second time-averaged absolute magnitude beingat least 100 gauss greater than the first time-averaged absolutemagnitude.
 13. The apparatus of claim 9, the second time-averagedabsolute magnitude being at least 125 gauss greater than the firsttime-averaged absolute magnitude.
 14. The apparatus of claim 9, whereinthe second time-averaged absolute magnitude is a maximum time-averagedabsolute magnitude of magnetic field strength around the toning shellouter circumference.
 15. The apparatus of claim 9, wherein the magneticcore is either fixed or rotatable.
 16. The apparatus of claim 9, whereinthe cylindrical toning shell is either fixed or rotatable.
 17. Theapparatus of claim 9, wherein the magnetic core is cylindrical,comprising an outer magnetic core circumference and a multitude ofmagnets of uniform strength with alternating north and south polesdisposed around the outer magnetic core circumference.
 18. The apparatusof claim 9, wherein the magnetic core is offset toward the cylindricaltoning shell such that the magnetic core is closest to the cylindricaltoning shell at the second location.
 19. The apparatus of claim 9,wherein the carrier particles comprise hard magnetic carrier particles.20. The apparatus of claim 9, wherein the toner particles comprise MICRtoner particles.
 21. An electrographic development apparatus,comprising: a film; a cylindrical toning shell having an toning shellouter circumference; a mixture of toner and carrier particles disposedon the cylindrical toning shell in contact with the film, thecylindrical toning shell being closest to the film at a first location,the mixture of toner and carrier particles being movable through thefirst location with a flow direction; and, a magnetic core disposedwithin the cylindrical toning shell that provides a magnetic fieldstrength of varying magnitude around the toning shell outercircumference, the magnetic field strength having a first time-averagedabsolute magnitude at the first location, and a second time-averagedabsolute magnitude at a second location a distance from the firstlocation in the flow direction, the second time-averaged absolutemagnitude being at least 2.5% greater than the first time-averagedabsolute magnitude.
 22. The apparatus of claim 21, the secondtime-averaged absolute magnitude being at least 5% greater than thefirst time-averaged absolute magnitude.
 23. The apparatus of claim 21,the second time-averaged absolute magnitude being at least 7.5% greaterthan the first time-averaged absolute magnitude.
 24. The apparatus ofclaim 21, the second time-averaged absolute magnitude being at least 10%greater than the first time-averaged absolute magnitude.
 25. Theapparatus of claim 21, the second time-averaged absolute magnitude beingat least 12.5% greater than the first time-averaged absolute magnitude.26. The apparatus of claim 21, wherein the second time-averaged absolutemagnitude is a maximum time-averaged absolute magnitude of magneticfield strength around the toning shell outer circumference.
 27. Theapparatus of claim 21, wherein the magnetic core is either fixed orrotatable.
 28. The apparatus of claim 21, wherein the cylindrical toningshell is either fixed or rotatable.
 29. The apparatus of claim 21,wherein the magnetic core is cylindrical, comprising an outer magneticcore circumference and a multitude of magnets of uniform strength withalternating north and south poles disposed around the outer magneticcore circumference.
 30. The apparatus of claim 21, wherein the magneticcore is offset toward the cylindrical toning shell such that themagnetic core is closest to the cylindrical toning shell at the secondlocation.
 31. The apparatus of claim 21, wherein the carrier particlescomprise hard magnetic carrier particles.
 32. The apparatus of claim 21,wherein the toner particles comprise MICR toner particles.
 33. Anelectrographic development method, comprising: moving a mixture of tonerand carrier particles disposed on a cylindrical toning shell in contactwith a film in a flow direction through a first location wherein thecylindrical toning shell is closest to the film, a magnetic core beingdisposed within the cylindrical toning shell that provides a magneticfield strength of varying magnitude around the toning shell outercircumference, the magnetic field strength having a first time-averagedabsolute magnitude at the first location, and a second time-averagedabsolute magnitude at a second location a distance from the firstlocation in the flow direction, the second time-averaged absolutemagnitude being greater than the first time-averaged absolute magnitude,a scavenger being adjacent the second location.
 34. The method of claim33, comprising rotating the magnetic core.
 35. The method of claim 33,comprising rotating the toning shell.
 36. The method of claim 33,wherein the carrier particles comprise hard magnetic carrier particles.37. The method of claim 33, wherein the toner particles comprise MICRtoner particles.
 38. An electrographic development method, comprising:moving a mixture of toner and carrier particles disposed on acylindrical toning shell in contact with a film in a flow directionthrough a first location wherein the cylindrical toning shell is closestto the film, a magnetic core being disposed within the cylindricaltoning shell that provides a magnetic field strength of varyingmagnitude around the toning shell outer circumference, the magneticfield strength having a first time-averaged absolute magnitude at thefirst location, and a second time-averaged absolute magnitude at asecond location a distance from the first location in the flowdirection, the second time-averaged absolute magnitude being at least 25gauss greater than the first time-averaged absolute magnitude.
 39. Themethod of claim 38, the second time-averaged absolute magnitude being atleast 50 gauss greater than the first time-averaged absolute magnitude.40. The method of claim 38, the second time-averaged absolute magnitudebeing at least 75 gauss greater than the first time-averaged absolutemagnitude.
 41. The method of claim 38, the second time-averaged absolutemagnitude being at least 100 gauss greater than the first time-averagedabsolute magnitude.
 42. The method of claim 38, the second time-averagedabsolute magnitude being at least 125 gauss greater than the firsttime-averaged absolute magnitude.
 43. The method of claim 38, comprisingrotating the magnetic core.
 44. The method of claim 38, comprisingrotating the toning shell.
 45. The method of claim 38, wherein thecarrier particles comprise hard magnetic carrier particles.
 46. Themethod of claim 38, wherein the toner particles comprise MICR tonerparticles.
 47. An electrographic development method, comprising: movinga mixture of toner and carrier particles disposed on a cylindricaltoning shell in contact with a film in a flow direction through a firstlocation wherein the cylindrical toning shell is closest to the film, amagnetic core being disposed within the cylindrical toning shell thatprovides a magnetic field strength of varying magnitude around thetoning shell outer circumference, the magnetic field strength having afirst time-averaged absolute magnitude at the first location, and asecond time-averaged absolute magnitude at a second location a distancefrom the first location in the flow direction, the second time-averagedabsolute magnitude being at least 2.5% greater than the firsttime-averaged absolute magnitude.
 48. The method of claim 47, the secondtime-averaged absolute magnitude being at least 5% greater than thefirst time-averaged absolute magnitude.
 49. The method of claim 47, thesecond time-averaged absolute magnitude being at least 7.5% gaussgreater than the first time-averaged absolute magnitude.
 50. The methodof claim 47, the second time-averaged absolute magnitude being at least10% gauss greater than the first time-averaged absolute magnitude. 51.The method of claim 47, the second time-averaged absolute magnitudebeing at least 12.5% greater than the first time-averaged absolutemagnitude.
 52. The method of claim 47, comprising rotating the magneticcore.
 53. The method of claim 47, comprising rotating the toning shell.54. The method of claim 47, wherein the carrier particles comprise hardmagnetic carrier particles.
 55. The method of claim 47, wherein thetoner particles comprise MICR toner particles.
 56. An electrographicdevelopment apparatus, comprising: a film; a cylindrical toning shelldefining a center of rotation; a mixture of toner and carrier particlesdisposed on the cylindrical toning shell in contact with the film, thecylindrical toning shell being closest to the film at a first location,the mixture of toner and carrier particles being movable through thefirst location with a flow direction; and, a magnetic core disposedwithin the cylindrical toning shell offset toward the cylindrical shellsuch that the magnetic core is closest to the cylindrical toning shellat a second location a distance from the first location in the flowdirection such that a line from the first location to the center ofrotation to the second location defines an acute angle greater than 20degrees.
 57. The apparatus of claim 56, the acute angle being at least30 degrees.
 58. The apparatus of claim 56, the acute angle being atleast 45 degrees.
 59. The apparatus of claim 56, the acute angle beingat least 60 degrees.
 60. The apparatus of claim 56, wherein the carrierparticles comprise hard magnetic carrier particles.
 61. The apparatus ofclaim 56, wherein the toner particles comprise MICR toner particles. 62.The apparatus of claim 56, wherein the cylindrical toning shell iseither rotatable or fixed.
 63. The apparatus of claim 56, wherein themagnetic core is either rotatable or fixed.
 64. An electrographicdevelopment method, comprising: moving a mixture of toner and carrierparticles disposed on a cylindrical toning shell in contact with a filmin a flow direction through a first location wherein the cylindricaltoning shell is closest to the film, the cylindrical toning shelldefining a center of rotation, a magnetic core being disposed within thecylindrical toning shell offset toward the cylindrical toning shell suchthat the magnetic core is closest to the cylindrical toning shell at asecond location a distance from the first location in the flow directionsuch that a line from the first location to the center of rotation tothe second location defines an acute angle greater than 20 degrees. 65.The method of claim 64, the acute angle being at least 30 degrees. 66.The method of claim 64, the acute angle being at least 45 degrees. 67.The method of claim 64, the acute angle being at least 60 degrees. 68.The method of claim 64, wherein the carrier particles comprise hardmagnetic carrier particles.
 69. The method of claim 64, wherein thetoner particles comprise MICR toner particles.
 70. The method of claim64, comprising rotating the cylindrical toning shell.
 71. The method ofclaim 64, comprising rotating the magnetic core.
 72. An electrographicdevelopment apparatus, comprising: a film; a cylindrical toning shelldefining a center of rotation; a mixture of toner and carrier particlesdisposed on the cylindrical toning shell in contact with the film, thecylindrical toning shell being closest to the film at a first location,the mixture of toner and carrier particles being movable through thefirst location with a flow direction, the mixture of toner and carrierparticles comprising hard magnetic carriers; and, a magnetic coredisposed within the cylindrical toning shell offset toward thecylindrical shell such that the magnetic core is closest to thecylindrical toning shell at a second location a distance from the firstlocation in the flow direction such that a line from the first locationto the center of rotation to the second location defines an acute anglegreater than 20 degrees, the magnetic core being rotatable.
 73. Theapparatus of claim 72, wherein the toner particles comprise MICR tonerparticles.